Food intake and physical activity for the average person is a debatable topic. Some research indicates that there are benefits to exercising on an empty stomach, while other evidence suggests that the negative effects may outweigh the benefits.
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Fat burn may increase if you work out without eating, but you also risk using muscle for fuel and limiting your exercise duration due to fatigue. Understand the facts; then consult your doctor or a professional regarding the best course of action for your condition.
Working out without eating first can lead to lightheadedness or low blood sugar. However, your body might react differently.
Fasting and Body Fat
Proponents of working out on an empty stomach suggest that this method causes the body to shift from primarily using carbohydrates for energy to burning more stored fat. However, a study published in 2014 by Journal of the International Society of Sports Nutrition looked at the effect of fasting, or exercising on an empty stomach, versus consuming a meal prior to exercise on body composition.
The findings of the study demonstrate that aerobic exercise along with a diet that produced a calorie deficit caused loss of body fat, regardless of the timing of meals.
Intensity Is Key
Working out on an empty stomach may be most effective when doing steady-state cardio. However, high-intensity exercises like heavy resistance training rely primarily on glucose for muscle contraction. If glucose stores are low after several hours of fasting, your body may break down your lean muscle mass for fuel, defeating the purpose of your workout.
Your training status, stores of intramuscular fat and the capacity of your muscles to store glucose in the form of glycogen are primary determinants of energy pathways during intense exercise.
Keep Your Mind Sharp
Exercising without eating first can lead to low blood glucose, which can interfere with your brain function. When you eat, glucose levels in your circulating blood rise and are available to travel to your muscle cells. Glucose is also available as glycogen stored in your muscles. When you work out before eating, glycogen and blood glucose can become quickly depleted, causing hypoglycemia.
Because glucose is the only fuel that your brain can use directly, low levels may cause lightheadedness, nausea, muscle fatigue and poor exercise performance. Regular ongoing training enhances your muscles' capacity to store glycogen.
Plan for Performance
Timing and quantity of food can influence your exercise performance. For optimal exercise capacity, follow these guidelines: If you eat a large meal, wait three to four hours before exercising. For a small meal, eat two to three hours pre-exercise. A snack is your best option, eaten an hour before exercise. Try consuming a piece of fruit, yogurt or granola before exercise to maximize blood glucose and calorie burn.
Eating a snack combining protein and carbohydrates immediately after exercise will replenish muscle glycogen stores, setting you up for your next workout. Drink plenty of water before and during your workout. Adequate hydration and replacement of electrolytes are also critical for peak exercise performance.